A fuel cell is a device wherein fuel (reducing agent) and oxygen or air (oxidizing agent) are continuously supplied from the exterior to be reacted electrochemically, thereby to produce electrical energy, and fuel cells are classified based on their operating temperatures, kinds of using fuel, applications and so forth. On the other hand, recently, they are, in general, roughly classified into five kinds, i.e. a solid oxide fuel cell, a molten carbonate fuel cell, a phosphoric acid fuel cell, a polymer electrolyte fuel cell, and an alkaline aqueous solution fuel cell, mainly depending on kinds of using electrolytes.
These fuel cells are of the type using hydrogen gas produced from methane etc. as fuel. Recently, however, there is also known a direct methanol fuel cell (hereinafter also referred to as DMFC) wherein a methanol aqueous solution is directly used as fuel.
Among them, attention has been paid to a solid polymer fuel cell (hereinafter also referred to as PEFC) having a structure wherein a solid polymer membrane is sandwiched between two kinds of electrodes, and further, these members are sandwiched between separators.
In general, this PEFC is in the form of a stack structure wherein a plurality of unit cells each having electrodes arranged on both sides of a solid polymer membrane, respectively, are stacked so as to increase an electromotive force thereof depending on the purpose. A separator disposed between the unit cells is generally formed on one side thereof with a fuel gas feed groove for feeding fuel gas to one of the adjacent unit cells. In case of such a separator, fuel gas and oxidant gas are supplied along the surfaces of the separator.
As the PEFC separators, there are known a separator obtained by planing a graphite board and applying a grooving process thereto, a molded separator of a carbon compound obtained by kneading carbon into resin, a metal separator applied with a grooving process by etching or the like, a separator wherein the surface of a metal material is coated with anticorrosive resin, and so forth. These separators are each formed with a fuel gas feed groove and/or an oxidant gas feed groove according to requirements.
Like a fuel cell for a portable terminal, for example, there are also those instances where an electromotive force is not required so much, but it is required to be of the flat type and as thin as possible, other than the fuel cell of the stack structure. However, there has also been a problem that the feeding of fuel and oxygen becomes uneven depending on places in case of the flat type wherein a plurality of unit cells are arranged in a flat manner and electrically connected in series.
In view of this, for improving this unevenness of the fuel feeding, there has been considered a separator having a structure wherein many through holes are formed in a perpendicular direction relative to a surface of the separator contacting a membrane electrode assembly (MEA), and fuel and oxygen are fed via the through holes.
Herein, an assembly including electrode portions located between a fuel-feed-side separator of a fuel cell and an oxygen-feed-side separator thereof, for example, an assembly such as a membrane composed of a collector layer, a fuel electrode, a polymer electrolyte, an oxygen electrode, and a collector layer that are stacked in the order named, is called a membrane electrode assembly (MEA).
However, if the separator having the foregoing structure is formed, for example, only from a metal material, it is necessary to increase a thickness of the separator in view of strength so that reduction in weight of a fuel cell becomes difficult.
As described above, in recent years, the possibility has been increased for the fuel cells to be widely used and, in case of the PEFC, there has also been required such a one that is of the flat type and as thin as possible. However, with respect to the separator, sufficient strength and further reduction in weight have been required, and further, there has been required such a one that has a sealing function for preventing fuel, moisture etc. inside a cell from leaking out to the exterior of the cell from portions other than a fuel feed surface when it is employed in a polymer electrolyte fuel cell.